Begin by preheating your oven to 350°F (175°C). Lightly grease a 9x9-inch baking dish with cooking spray or a little oil to prevent sticking.
In a large mixing bowl, combine the rolled oats, baking powder, ground cinnamon, and salt. Stir gently to mix the dry ingredients thoroughly, then set this bowl aside.
In a separate mixing bowl, whisk together the almond milk, brown sugar (or maple syrup), applesauce, and vanilla extract until all ingredients are well incorporated and smooth.
Carefully pour the wet mixture into the bowl containing the dry oats. Stir gently until just combined; be cautious not to overmix.
Gently fold in the diced apples, chopped nuts (if using), and raisins or dried cranberries (if desired) until evenly distributed throughout the mixture.
Pour the oatmeal mixture into the prepared baking dish, spreading it evenly across the bottom.
Place the baking dish into the preheated oven and bake for 30-35 minutes. The top should appear golden brown and the oatmeal should be set.
Once baked, remove the dish from the oven and allow it to cool for about 5 minutes before slicing into squares for serving.
Notes
Serve warm, drizzled with honey or maple syrup, and garnish with fresh apple slices.